Apparatus and method for indirect surface cleaning

ABSTRACT

A method for laser surface cleaning of a target surface that has limited or no access to the environment directly above the surface to be cleaned. The method includes the ability to clean the surface with a reduced risk of substrate damage. The method includes direct laser excitation of a contaminated substrate surface and thermal transfer from the substrate to the contaminating particulate or contamination layer. The method also includes producing a thermally based removal and reducing a risk of substrate damage by keeping the temperature required to produce surface cleaning below the thermal damage level of the substrate material. In addition, the method includes reducing the risk of substrate damage by utilizing relatively long pulse-widths, providing for improved removal of small contaminants/particles, and directing the beam through a material disposed relative to the surface that is part of the substrates environmental enclosure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to provisional U.S. patent applicationentitled, APPARATUS AND METHOD FOR INDIRECT SURFACE CLEANING, filed Aug.9, 2007, having a Ser. No. 60/954,989, disclosure of which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods useful incleaning surfaces. More particularly, the present invention relates todevices and methods useful in cleaning surfaces of components typicallyused in the semiconductor industry, optics, etc. The devices and methodsdisclosed are applicable to extending the useful life of photomaskreticles.

BACKGROUND OF THE INVENTION

Electromagnetic radiation has long been used for surface cleaning.Examples of these processes include the removal of surfacecontamination, removal of thin material layer coatings such as paints orremoval of oils from metal work surfaces. Some of the earliest examplesutilized flash lamp radiation sources. These systems can be limited inapplication because of peak powers achievable.

have increasingly been used for these types of processes because of thehigh peak powers achievable, high energy stability and wavelengthselectivity. These features allow for high localization, improvedmaterial selectivity, and depth control of the cleaning effect. Lasersurface cleaning processes can be broadly categorized into surfacecontamination layer removal and particulate removal. Removal of surfacecontamination layers is normally accomplished by laser ablation.Particle removal involves removing the contamination as a whole.

Cleaning processes under both categories can benefit from the use ofpulsed laser radiation to provide higher peak powers. Short pulsedradiation in particular can provide improved processing. Short pulsedradiation has been shown to decrease the heat affected zone in laserablation processing. This allows improved localization of the ablativeremoval as well as finer control of the removal depth. Short pulseradiation also can enhance particulate removal by increasing the rate ofthermal increase within the particles and/or substrate therebyincreasing the acceleration forces that produce particle removal.

Substrate damage can be an issue for both ablative and particulateremoval processes and several techniques have been developed to minimizethese effects. For ablative processes, selecting a wavelength thatincreases the absorption of the contaminant can reduce the fluencerequirement and therefore reduce substrate damage. In addition, usingmultiple pulses for full contaminant removal can reduce the requiredfluence. However, substrates that have high absorption at the selectedwavelengths are likely to be ablated along with the contamination, evenwith wavelength selection and multiple pulse removal processes. Theability to end stop the removal process at the substrate interface willbe limited in these cases. This problem is significantly increased forsmaller size contamination, since the absorption cross section for thecontamination is reduced relative to the substrate.

As with ablative removal processes, particulate removal processes canalso cause substrate damage for sensitive substrates and substrates thathave high absorption at the processing wavelength. This problem isincreased for small particle removal because of increased adhesionforces between the particles and substrate and self focusing of thelaser underneath the particles. For particle cleaning processes, thedeveloped devices and methods for reducing the risk of substrate damageinvolve controlling the environment above the contaminated surface.Examples of particulate laser processes allowing reduced fluence levelsinclude wet laser cleaning, steam laser cleaning, and increased humiditycleaning. Combinations of laser and other cleaning processes (includingetching, organic solvents, and ultrasonic) have been shown to increasecleaning effectiveness and may reduce the risk of substrate damage.However, with the exception of dry laser cleaning processes, all of theparticulate removal processes described require access to theenvironment above the substrate surface. This may be impractical forsome systems.

Alternative dry laser particulate cleaning processes have beendeveloped. Laser acoustic wave cleaning and laser shock wave cleaningare dry laser cleaning methods that have also been evaluated forparticulate cleaning. Laser acoustic wave cleaning involves directexcitation to the substrate and therefore suffers from a high potentialfor substrate damage particularly for small particles as discussed.Laser shock wave cleaning has been shown to improve particulate removaland can reduce the risk of substrate damage by focusing the laser abovethe substrate surface and relying on the shock wave interaction with theparticulates. This technique will also have increased difficulty whenapplied to small particle removal. In addition, the shock wave maydamage other sensitive features on or near the surface of the substrate.This is particularly true if there is a sensitive material above thesubstrate surface, since generating the shock wave requires relativelyhigh laser intensity focused above the substrate.

Even the newest dry laser techniques can also be limited in cases whereaccess to the environment above the surface is not practical (e.g.,enclosed systems). The removal process will only move the particle to adifferent location on the substrate for an enclosed system, because theparticles are removed from the surface as a whole. Typically thesetechniques utilize additional control devices and methods to completelyremove the particles from the substrate being cleaned. These methodsinclude directed air flow, use of reduced pressure (vacuum) or gravitymost of which require open access to the environment above the substratesurface.

Semiconductor manufacturing is one of the major industrial areas thatutilize surface cleaning processes including laser cleaning methods.Many of the required cleaning processes have a stringent tolerance onthe allowable level of substrate damage. In addition, the small productfeatures make it necessary to remove very small particles to avoidproduct failures. Cleaning is an issue in multiple wafer processingsteps and includes extended contamination layer (e.g., resist removal)and particulate contamination removal.

Surface cleaning is also a requirement for the optics (e.g., photomasks)used in the wafer manufacturing process. For photomasks in particular, abuild up of contamination is observed during the normal usage of themasks in the wafer print processes. These masks are exposed to deepultraviolet (DUV) radiation during the normal processing used inprinting the mask pattern onto the wafer. Exposure to this radiationproduces a contamination growth in the form of small particles thatabsorb the illuminating radiation. This growth is commonly referred toas haze.

Haze formation is a problem for the wafer print process because as theparticles increase in size they block more of the light beingtransmitted through the photomask. Eventually the haze contaminationabsorbs enough of the light to cause defects in the printed image of thephotomask on the wafer. Before the haze contamination reaches thislevel, the photomask surface must be cleaned. This cleaning requirementhas the effect of decreasing the useable lifetime of a photomask becausethe processes currently used to remove haze deteriorate the absorbingfilm on the mask. For partial absorbing films, the current cleaningmethods reduce the film thickness and therefore affect the filmstransmission and phase properties. Changes in phase and/or transmissionreduce reticle lifetime by altering the size and shape of printedfeatures on the wafer beyond acceptable tolerances. Duplicate sets ofphotomasks must be made in order to continue manufacturing once theuseable life of a photomask is exceeded. Duplicate sets are alsorequired for use while contaminated photomask are being cleaned. Therecan be a several day time requirement before the mask is cleaned andverified, since the cleaning processes are typically preformed at adifferent facility. As the required feature size for semiconductormanufacture decreases, the size of haze growth that will produce printeddefects also decreases. This increased sensitivity to haze growth meansthat the newest photomasks will need to be cleaned more frequently andwill have a shorter useable life.

Application of alternative cleaning methods to remove photomask surfacehaze contamination is hindered by the use of pellicles attached to thephotomask surface(s). A pellicle consists of a frame that is adhesivelybonded to the photomask surface and a thin membrane stretched across thepellicle frame. Pellicles are used to prevent externally generatedparticles from settling onto the surface of the photomask where theycould affect the print process. Externally generated particles settle onthe membrane above the mask surface where they have a significantlyreduced affect on the print process. With the exception of a smallfilter valve on the pellicle frame to allow for pressure equalization,the top surface of the photomask is effectively sealed from the localenvironment by the pellicle attachment.

The current accepted method for haze removal requires the wafermanufacturer to ship the contaminated photomask back to the mask makeror to a third party. Here the pellicle frame is removed from thephotomask, the mask is cleaned, inspected for defects and a new pellicleis attached to the photomask and in many cases the mask is inspectedagain for particle defects before it is shipped back to the wafermanufacturer. This typically takes days to complete, increases thephotomask cost due to the additional processing and degrades thephotomask quality due to the cleaning process. Additionally, there is asmall probability, usually due to the adhesive from the pellicle beingremoved and falling onto printable areas of the photomask, that the maskwill be damaged beyond use by the haze removal process.

Current efforts to improve the issues related to haze growth onphotomasks have focused on processes that can be implemented before thepellicle is added because of the difficulties related to throughpellicle cleaning. These efforts have been primarily focused on surfacepreparation and use of alternate chemicals in the cleaning processes.The latter has been shown to change the haze contamination species butnot eliminate their growth. Both areas, at best, show a reduction in thegrowth rate and do not eliminate the requirement for cleaning. Morerecently, use of an inert environment has been shown to decrease thegrowth rate of haze formation on photomasks. Application of this methodrequires control of all environments the photomask is exposed toincluding all process equipment. As with other methods being developed,this process has the potential to reduce the growth rate but noteliminate the requirement for and the detrimental effects of cleaning.

SUMMARY OF THE INVENTION

At least in view of the above discussion, it would be advantageous todevelop an alternative cleaning method and/or apparatus for removinghaze contamination from a photomask surface that avoids the detrimentaleffects of the current cleaning processes.

It would be additionally advantageous to develop a novel laser basedcleaning method and/or apparatus for removing haze contamination from aphotomask surface without pellicle removal, because of the limitedapplicability of demonstrated laser based cleaning methods.

It would be additionally advantageous to integrate methods and/orapparatuses for removing haze contamination from a photomask surfaceinto a wafer fabrication process.

It would be additionally advantageous to develop a method and/orapparatus for removing haze contamination from a photomask surface thatis minimally dependent or independent of particle/contamination size.

It would be additionally advantageous to develop a method and/orapparatus for removing haze contamination from a photomask that wouldproduce minimal or no substrate and absorbing film material changes andresult in an extended lifetime of the photomask.

It would be additionally advantageous to develop a method and/orapparatus to extend the lifetime of a photomask by modifying or alteringthe phase of a partial absorbing film on the photomask.

It would be additionally advantageous to develop a method that wouldmitigate haze re-growth or reformation.

The foregoing needs are met, to a great extent, by certain embodimentsof the present invention. According to one embodiment of the presentinvention, a method for laser surface cleaning with a reduced risk ofsubstrate damage is provided. The method includes the direct laserexcitation of the contaminated substrate surface and thermal transferfrom the substrate to the contaminating particulate or contaminationlayer (e.g., by convection or conduction). The resulting temperatureincrease in the contamination produces a thermally based removal,including but not limited to vaporization and decomposition. The methodhas a reduced risk of substrate damage because the temperature requiredto produce surface cleaning is below the thermal damage level of thesubstrate material(s). The risk of substrate damage is also reduced overother techniques because it can utilize relatively long pulse-widthswhich reduce the potential for multi-photon absorption processes. Themethod provides for improved removal of small contaminants/particlesbecause it has a minimal dependence on particle size. The methodprovides particular advantages, for applications where the environmentabove the contaminated substrate is substantially or full enclosed. Inthese cases, the method may also include directing the beam through amaterial disposed relative to the surface that is part of the substratesenvironmental enclosure. For example, the inventive method could be usedto clean haze contamination from the surface of a pellicalizedphotomask.

According to another embodiment of the present invention, an apparatusfor laser surface cleaning utilizing the above-described method isprovided. The apparatus may include metrology for inspection of surfacecontamination and material property analysis before, during, and/orafter the cleaning process.

The apparatus may also include components for controlling thetemperature of the substrate and/or adjacent materials. These componentsmay include, for example, local temperature control or overalltemperature control

According to yet another embodiment of the present invention, a waferfabrication process utilizing the above-discussed method and/or theabove-discussed apparatus is provided for cleaning of contaminatedphotomask surfaces. The fabrication process may include performing thecleaning steps within the wafer fabrication facility. According tocertain embodiments the use of a duplicate photomask in the waferfabrication process is not required while the original photomaskundergoes the dry laser cleaning cycle.

Certain embodiments of the present invention provide the ability toclean surfaces without surface preparation or environmental controlabove substrate surface. Certain embodiments provide dry laser surfacecleaning processes with reduced risk of substrate damage. Also, certainembodiments provide for minimal dependence on contamination size and/orthe ability to clean a photomask surface without pellicle removal.Further, certain embodiments of the present invention reduced photomaskcleaning time and/or provide for an extended lifetime of photomasks usedin wafer printing. In addition, certain embodiments of the presentinvention reduce wafer manufacturing costs including reduced number ofduplicate photomasks and/or reduce downtime during wafer manufacturing.

There has thus been outlined, rather broadly, certain embodiments of theinvention in order that the detailed description thereof herein may bebetter understood, and in order that the present contribution to the artmay be better appreciated. There are, of course, additional embodimentsof the invention that will be described below and which will form thesubject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of embodiments inaddition to those described and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein, as well as the abstract, are for thepurpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Attached are a plurality of figures that illustrate various embodimentsof the present invention.

FIG. 1A illustrates a schematic diagram of laser excitation and surfacecontamination.

FIG. 1B illustrates a schematic diagram of substrate surfaceillustrating contamination removal. According to certain embodiments ofthe present invention, multiple species may be removed from the mask andthese species may be in the form of a gas, liquid, solid, etc.

FIG. 2 illustrates a diagram of a photomask surface with thin filmabsorber on top including contamination on the film and on thesubstrate.

FIG. 3 illustrates a plot of a quartz absorption spectrum from the deepultraviolet to the far infrared region of the electromagnetic spectrum.

FIG. 4 illustrates a diagram of a photomask surface with thin filmabsorber including pellicle attached to surface. According to certainembodiments of the present invention, there can be contamination on thefilm and/or on the substrate.

FIG. 5A illustrates a schematic diagram of a photomask with a pellicleshowing a laser beam focused through the pellicle and onto a surface.

FIG. 5B illustrates a schematic diagram of the beam spot size on thepellicle versus on the mask produced by focusing.

FIG. 5C illustrates a schematic diagram of a photomask with a pellicleshowing laser beam focused through the pellicle and onto the surface anda side view of the beam spot on the pellicle.

FIG. 6A illustrates a cross sectional view of a gaussian beam energydistribution and the corresponding temperature profile produced.

FIG. 6 b illustrates a cross sectional view of a top-hat beam energydistribution and the corresponding temperature profile produced.According to certain embodiments of the present invention, gaussian,flat top, and/or top hat energy distributions may be used.

FIG. 7 illustrates a diagram of a photomask with a cold plate contactingbottom of the mask. According to certain embodiments of the presentinvention, the contact point could be, for example, either water (orother liquid or gas) flow through the cold plate or electrical contactfor thermoelectric cooling.

FIG. 8 illustrates a diagram showing force air cooling of areas on thephotomask. According to certain embodiments of the present invention,airflow is directed at the pellicle frame.

FIG. 9A illustrates a diagram showing a single pass of the laser beamacross surface to minimize local thermal build up. A single row orcolumn with large lateral spacing between spots is illustrated.

FIG. 9B illustrates a diagram showing two passes of the laser beamacross surface to minimize local thermal build up. A single row with twosets of beam spots overlapped with large spacing between sets of pulsesis illustrated.

FIG. 9C illustrates a diagram showing multiple laser passes over an areaof the substrate to achieve complete cleaning of the section of thesubstrate.

FIG. 9D illustrates a diagram illustrating a second dimension of surfacecleaning.

FIG. 9E illustrates a diagram representing the use of non-contiguouspulses on the surface

FIG. 10 illustrates a diagram illustrating the use of laser pulsepattern to control the location of residual materials.

FIG. 11A illustrates a diagram illustrating the use of gravity tocontrol the location of residual materials.

FIG. 11B illustrates a diagram illustrating the use of gravity tocontrol the location of residual materials.

FIG. 12 illustrates a schematic diagram of contaminated substratesurface with thermocouple or infrared temperature monitoring devices.

FIG. 13 illustrates a schematic diagram of contaminated substratesurface with imaging, microscopy, spectroscopy, or combination systemfor contamination analysis.

FIG. 14 illustrates a schematic diagram of a contaminated substratesurface with imaging system where the imaging system and laser beamdelivery are common path.

FIG. 15 illustrates a system diagram showing robotic load and X/Y/Zstage motion of substrate relative to laser beam.

FIG. 16A illustrates a box diagram of typical wafer fabrication processutilizing photomask wet clean processing.

FIG. 16B illustrates a box diagram of a wafer fabrication process flowincorporating use of laser photomask cleaning without pellicle removal.

FIG. 16C illustrates a box diagram of a wafer fabrication process flowincorporating use of laser photomask cleaning without the use ofadditional mask sets during the clean process.

DETAILED DESCRIPTION

The invention will now be described with reference to the drawingfigures, in which like reference numerals refer to like partsthroughout. According to certain embodiments of the present invention, amethod for laser surface cleaning with a reduced risk of substratedamage is provided.

FIG. 1A illustrates an embodiment of the present invention in which anexcitation energy 2 comes from an energy source, such as a laser 1 andis directed towards the contaminated substrate's 4 surface resulting inthermal transfer from the substrate's 4 surface to the contaminatingparticulate 3 or contamination layer (e.g., by convection orconduction). However, energy sources other than laser may also be used(e.g., lamps and other devices that can radiate energy all along theelectromagnetic spectrum may be used, including generators or x-rays,microwaves, infrared radiation, near-ultraviolet radiation, etc.). Also,the surface may be of any material (e.g., the surface of a siliconwafer). The resulting temperature increase in the contaminationtypically produces a thermally based removal and its effects are shownin FIG. 1B, including but not limited to vaporization particles 6 anddecomposition particles 5. Additionally, the contaminating particulate 3can be found on photomask as illustrated in FIG. 2, which showscontaminating particulates 3 on substrate 4 and on a thin film absorber7.

According to certain embodiments of the present invention, the methodhas a reduced risk of substrate damage because the temperature typicallyused to produce surface cleaning is below the thermal damage level ofthe substrate 4 material(s) 4. The risk of substrate damage is alsotypically reduced over other techniques because it can, in someinstances, utilize relatively long pulse-widths which often reduce thepotential for multi-photon absorption processes.

The above-discussed exemplary method generally provides for improvedremoval of small contaminants/particles because it has a minimaldependence on particle size. The method may be particularly advantageousfor applications where the environment above the contaminated substrateis substantially or fully enclosed. In these cases, the method may alsoinclude directing the beam through a material disposed relative to thesurface that is part of the substrates environmental enclosure. Forexample, the inventive method could be used to clean haze contaminationfrom the surface of a pellicalized photomask.

It has been suggested that decomposition of a contaminant species couldbe an advantage in a laser surface cleaning process. However, beforeembodiments of the present invention were developed, there had been nodisclosure of a process that utilizes laser heating of a substrate toproduce thermally based surface cleaning.

According to certain embodiments of the present invention, the methodincludes selecting a laser wavelength that substantially coincides witha strong absorption of the substrate and setting the laser energy andpulse width to produce the desired cleaning effect. Increased absorptionin the substrate, in some instances, allows lower laser energies for thecleaning process. Therefore decreasing the potential for damage toadjacent materials that may interact with the laser as it is directed toor reflected from the surface. Although not a requirement, according tocertain embodiments of the present invention, a wavelength is selectedthat is also highly absorbed by the contaminant or contaminants, sincethis may improve the desired thermal removal effect. The use of multiplelaser wavelengths and/or laser energies may be used in the cleaningprocess, particularly when the substrate consists of more than onematerial. Multiple laser energies may also be used for the samecomponent, typically if it undergoes a material or material propertieschange during a first step of the desired cleaning process. Multiplewavelengths may be produced, for example, by utilizing multiple lasersources or a single tunable laser source or both. Multiple energies canbe used by control of the laser source(s) output energy using controlsinternal or external to the laser(s).

Practical Example

The following is an example of a method according to one embodiment ofthe present invention applied to surface cleaning of haze contaminationfrom photomask substrates used in wafer fabrication processes. Thisexample may be used throughout the additional embodiments of theinventive method discussed.

Certain embodiments of the present invention are applicable to thesurface cleaning of wafers (e.g., silicon wafers). A type of haze growthhas also been observed for these substrates and can become an issue insome instances if it is not removed prior to wafer printing. Use ofenvironmental control has been suggested for the control of haze growthon silicon wafers. However, certain embodiments of the present inventionare for haze mitigation or other types of contamination removal onsurfaces, for example, silicon wafers. More specifically, according tocertain embodiments of the present invention, by laser exciting thesilicon wafer substrates below the thermal damage threshold it ispossible to remove the haze.

Methods according to certain embodiments of the present invention canclean contamination precursor materials, because such methods typicallydo not rely on a direct absorption of the material disposed on thesubstrate. In this way, a method according to certain embodiments of thepresent invention may act as a surface preparation technique thatreduces the rate of contamination formation. Photomask haze growth, forexample, can be reduced by applying a method according to the presentinvention prior to use in the wafer fabrication process and removing orrelocating haze growth precursor materials (e.g., acid residue, water,etc.) or nucleation sites. Other techniques could be used in conjunctionwith the current invention to further mitigate regrowth or reformationof haze after the reticle is processed with the present invention. Forexample, surface preparation prior to pellicalization or environmentalcontrol prior to, during, or after processing could increase reticlelifetime by reducing the haze regrowth or reformation rate.

Application of methods according to certain embodiments of the presentinvention to a substrate consisting of multiple materials may requireconsideration of the material parameters as well as the beam parameters,including excitation wavelength selection. The basis of the cleaningprocess makes it particularly desirable for all contaminated areas of asubstrate to reach a temperature substantially near that typicallyneeded for removal without exceeding the thermal damage threshold of thesubstrate. It is possible that the laser energy typically required tobring one of the materials to process temperature will produce thermaldamage in the other material, particularly if there is a significantdiscrepancy between the material absorptions. The local fluence of thebeam may be controlled based on the materials being exposed.

According to certain embodiments of the present invention, longer laserpulse widths, up to and including continuous wave (CW) lasers, are usedto improve the thermal equilibrium between materials with significantlydifferent absorption constants. However, the use of such longer laserpulse widths produce the highest thermal increase in the system and maynot be useable if a material adjacent to the substrate surface has athermal damage threshold below the process temperature.

According to certain embodiments of the present invention, a laserwavelength that has a significant absorption in all of the materials onthe substrate is selected. The same laser energy can then, for example,be used to produce the desired process temperature below any of thesubstrate materials damage thresholds. By considering the thermalproperties (including diffusivity) it is possible to take advantage ofthe thermal transfer between the different materials. This, in somecases, allows the use of a reduced process fluence to achieve removal onthe entire substrate, particularly if the thermal energy flow from ahigher absorbing material is preferential to the lower absorbingmaterial.

Control of the beam parameters is particularly desirable in theembodiments of the invention related to photomask surface cleaning ofhaze contamination. Wavelength selection, for example, is highlydesirable because of the physical structure of the typical photomask.Referring to FIG. 2, a photomask usually consists of a quartz substrate4 with a thin absorbing film 7 on the critical surface. In the case of ametal film, there will typically be a significant absorption coefficientfor the majority of producible laser wavelengths. For the quartzsubstrate, however, there will generally be a limited wavelength rangewhere the substrate has significant absorption and laser sources arecommonly available. Considering the thermal properties of the quartzversus the metal layer, certain processes according to embodiments ofthe present invention would utilize a wavelength that is highly absorbedby the quartz substrate material because thermal transfer between thematerials will occur preferentially from quartz to the metal layer.

The above discussion is also generally true for the case of partialabsorbing photomask films. In general, thermal flow for photomasks withpartially absorbing films will occur preferentially from the quartz tothe film, since the films typically contain a metal component and quartzhas a relatively low thermal diffusivity. However, there may bewavelength regions where these films do not significantly absorb unlikefor pure metal films. This has the potential for increasing the range ofwavelengths that could be used to preferentially excite the quartzsections of the substrate. In addition to thermal flow, thermally inducematerial changes (e.g. Oxidation, annealing, etc.) must be consideredfor partial absorbing films. The phase and transmission characteristicsof these materials are critical to their functioning and may be alteredby thermal processing. If a thermal material change produces an adverseaffect to the film performance, it may be necessary to limit the maximumtemperature of the removal process. If a thermal material changeproduces an advantageous affect it may be necessary to control theprocess uniformity by pulse shaping or pulse overlap.

A specific example of a representative method according to the presentinvention is the removal of ammonium sulfate haze from the surface of aphotomask. Temperatures and other regions—Ammonium sulfate is expectedto decompose at temperatures above 280° C. The lowest thermal damagepoint for a typical photomask will typically be the melting/reflow pointfor the base quartz substrate (i.e., around 1600° C.). Therefore, thereis a potential process where the temperature for contaminationremoval/cleaning can occur that is below the damage level of thesubstrate materials.

It is important to note that the exact species being removed from thephotomask typically only determines the process temperaturerequirements. Although it may be advantageous to have a significantabsorption in the contamination, it is not a requirement. As discussedabove, the relative absorption of the substrate materials is generallyconsidered because of potential differences in the material absorptioncharacteristics. In particular, it would be desirable that the quartzsubstrate have a significant absorption at the process wavelengthprimarily because the thermal flow will be preferential to the absorbingfilms.

Quartz substrates used for photomasks are typically specificallydesigned to have high transmission in the deep ultraviolet (DUV)wavelength range as show in the quartz absorption spectrum in FIG. 3.This is typically accomplished by using synthetically formed substratesthat have an extremely low level of impurities. With the exception of arelatively weak absorption near 3 μm wavelength, these materialstypically have high transmission in the infrared region as well. Themain absorption for these substrates generally occurs either below 0.2μm wavelength or above 8 μm wavelength. The shorter wavelengths are notin a particularly desirable wavelength range, because they are usuallysignificantly absorbed by air and because they have higher photon energyand are more likely to produce multiphoton processes.

Selecting a wavelength above 8 μm, for example near the 9 μm quartzabsorption, is particularly desirable according to certain embodimentsof the present invention. This typically produces a high absorption inthe quartz substrate without high environmental absorption. Particularlyif the photomask has a metal film layer (e.g., chrome), this wavelengthhas an additional benefit because the reflectivity of the metal filmincreases with increasing wavelength in this region. This typicallyreduces the light available to be absorbed by the film and generallyimproves the bias of the thermal excitation to the quartz. Thiswavelength may also provide an advantage for photomasks that have apartially absorbing film coating (i.e. MoSi) because the relatively highabsorption coefficient for quartz. Generally, the film materialtemperature reached at constant fluence should be similar to that forquartz because of the high quartz absorption and the higher thermaldiffusivity of the partial absorber compared to quartz. This is expectedto be true even if the partially absorbing film has a relatively highabsorption coefficient in this wavelength range.

The process just described for use according to certain embodiments ofthe present invention typically increases the useable lifetime of aphotomask by replacing the current cleaning processes used to removehaze from photomask surfaces. Unlike the typical chemical cleanprocesses used for haze cleaning, the laser removal process according tocertain embodiments of the present invention, does not generallydecrease the absorber thickness and/or line widths of the absorber film.Since material loss is a consequence of conventional cleaning methods,there is a limit to the number of “clean processes” that can beperformed before the photomask will no longer be usable. Additionally,the lifetimes for partially absorbing photomasks are also shortened byuse of these haze removing cleaning materials, since photomaskperformance is critically dependent on phase and transmission.Therefore, an unlimited number of cleaning cycles could be used with thelaser clean process according of the present invention.

It has been determined that employing temperatures below a criticalrange can produce a material change in a partially absorbing film. Forexample, a partially absorbing MoSi film anneals at a first temperatureand the affect of annealing the film is a reduction in the phase delayof the light transmitted through the film or a significant loss intransmission, it will be necessary operate the cleaning process belowthis first temperature. Otherwise, the lifetime of the partiallyabsorbing film photomask will be reduced as it is with the nominal wet“clean process” currently used for haze removal. However, thetemperature of the process of the current invention can be finelycontrolled by adjusting the energy provided to the surface (e.g.Controlling pulse duration, pulse amplitude, CW energy, etc.) andthereby circumvent the film's critical temperature tolerances.

However, if the affect of annealing the film is an increase in the phasedelay of the light transmitted through the film and minimal or no lossin transmission, operating the clean process above this firsttemperature, it will be advantageous. These processes are integral tothe production of the photomask and can produce an unacceptable lowphase delay even prior to use. In addition, it is possible that wetclean processing will be required in addition to use of the currentinvention. For example, if non haze related defects exist or appear onthe photomask a wet clean process may be required. Producing a materialchange in a partial absorbing film during the inventive clean processcould extend the lifetime of the photomask, by recovering phase delaylost by wet cleaning processing. It is also possible that thermalmodification to a partial absorbing film, using the inventive method,could by itself (without requirement for haze cleaning) extend thelifetime of a photomask reticle by recovering phase lost during wetclean processing.

One of the reasons that aggressive wet clean processes are used is thefact that removal of the pellicle frame from the photomask leaves anadhesive residue. Wet clean processes in general will affect theadhesive residue causing the adhesive to contaminate working areas ofthe mask, because they are generally difficult to localize. Some of thelaser clean processes disclosed herein, however, can be localized awayfrom the adhesive residues leaving them unaffected. A controlled removalof the pellicle frame and majority of adhesive followed by a laser cleanprocess according to an embodiment of the present invention allows asubsequent pellicle attachment without a wet clean requirement(aggressive or otherwise). This is particularly true if the laser cleanprocess according to an embodiment of the present invention is combinedwith the use of a multiple part pellicle that would utilize analternative bonding method or would not require exposure of the adhesivefor pellicle exchange.

Methods according to certain embodiments of the present invention may beapplied to photomask haze cleaning and do not require removal of thepellicle. These laser cleaning methods are typically performed throughthe pellicle film material without affecting the pellicle filmcharacteristics is illustrated in FIG. 4 showing a pellicle 8, apellicle frame 9 and substrate pellicle adhesive 10.

In this case, the absorption of the pellicle film 8 at the processwavelength and the energy density (fluence) at the substrate's 4 surfaceis typically considered. As with the substrate 4 and the substrate filmcoating 7, the cleaning process generally does not produce a temperatureincrease in the pellicle film that is above the damage threshold.Depending on the pellicle film however, there may be significantabsorption in the pellicle film near 9 μm absorption peaks for thequartz substrate. However, it is still possible to operate in a regionof significant pellicle film absorption because the pellicle film ispositioned above the substrate surface.

FIG. 5A illustrate focusing the excitation energy 2 through the focuslens 11 producing a converging beam 12 through the pellicle film ontothe substrate film coating 7 located on substrate's 4 surface to removecontaminating particulates 3. Wavelength and convergence propertiespermit focusing at different elevations and can reduce the relativetemperature increase in the pellicle film 8. The temperature increase inany substance is proportional to the fluence applied to the surface;ΔT˜F  Equation 1where ΔT is the temperature change within the material and F is theabsorbed laser fluence.

For a constant intensity or beam pulse energy, the fluence is inverselyproportional to the square of the beam spot radius.F˜E/r2  Equation 2where F is the fluence, E is the energy and r is the radius of the beamon the substrate surface.

FIG. 5B illustrates the spot beam size on a pellicle. The ratio of thebeam radius at the pellicle (pellicle beam 14) to the beam radius on themask surface 4 (mask beam 13) is typically increased by focusing thebeam through the pellicle and, therefore, the relative fluence on thepellicle film compared to the photomask substrate surface can bereduced. FIG. 5C is a side view showing the convergence at the surface 4at the mask beam 13 point versus the non-converged energy at thepellicle′ 9 entry point (pellicle beam 14).

In addition to wavelength considerations, utilizing processes thatproduce a large temperature increase in the system (e.g., long pulselength or high repetition rate) may be limited by the damage thresholdof the pellicle film. This is typically below the process temperaturerequirement for many photomask haze components.

Pulse Shaping

The pulse width, temporal pulse shape and the spatial distribution ofthe laser may be used to enhance the cleaning process or increase thesafe operation range for processing according to certain embodiments ofthe present invention. Shorter pulse widths can be used to minimize theoverall thermal input to the system (substrate and contamination).Longer pulse widths can be used to maintain the process temperature foran extended period of time enhancing the completeness of the thermalremoval process. The temporal pulse shape can be used to control thetemperature rise within the contaminating species. A long temperaturerise can be used to produce an initial effect (e.g., melting) that wouldbe followed by a secondary effect (e.g., decomposition). A shorter risetime can, in some instances, enhance vaporization of the contaminantwhile limiting the decomposition processes. Combinations of short andlong temporal pulse shape can also be used to optimize the removalprocess. The use of multiple pulses can also be used to lower the beamenergy that is desirable for complete cleaning, thereby furtherdecreasing the risk of substrate damage.

The spatial distribution of the laser beam can be used to increase theprocess window. For example, FIG. 6A shows a typical Gaussian spatialdistribution 15, that may produce a temperature gradient in thesubstrate 16 while FIG. 6B illustrates a flat top or top hat spatialdistribution 17 allowing for a more uniform temperature rise within thesubstrate 4. The spatial distribution can be used to increase theprocess window. For example, having a flat top or top hat spatialdistribution allows for a uniform temperature rise within the beam spot,whereas a Gaussian distribution typically produces a temperaturegradient within the beam spot in order to avoid risk of substratedamage, the maximum energy in the beam is typically limited by the peakof a Gaussian distribution. As described above, when more than onematerial exists on the substrate, longer pulse widths may be used toallow for thermal equilibration between substrate materials.

Thermal Management

Because certain embodiments of the present invention involve a thermalbased process, it is sometimes desirable to manage the overalltemperature of the system to avoid damage to thermally sensitive oreasily contaminated materials. This is particularly true in the case ofphotomask haze cleaning without pellicle removal. The pellicle filmstypically have a low thermal damage threshold. Therefore, it issometimes useful to avoid an overall system temperature build up thatmay transfer to and/or damage the pellicle material. This includes thepellicle frame and the enclosed environment between the mask surface andthe pellicle film.

Managing the system temperature can be accomplished in several ways. Thefollowing examples illustrate several representative methods of samplecooling and it is understood that other methods may exist. One way tomanage the system temperature is through contact cooling. The photomask,for example, may be placed in contact with a plate 17 that acts as aheat sink to draw the heat generated on the front surface of the masktoward the back of the mask is illustrated in FIG. 7 and include heatexchange pipes 18 and 19. This reduces the heat transfer to theenvironment above the mask surface, the pellicle film and the adhesivebetween the pellicle frame and the mask surface. The cooling can beaccomplished in a variety of ways, including flowing water or othercooling fluids or gases over the mask and/or pellicle, thermoelectriccooling or laser induced cooling of a portion or the entirety of themask and/or pellicle.

Another potential way to control temperature is through forcedconvection cooling. Filtered and/or cooled gas or liquid flow istypically directed onto portions of the mask, onto the pellicle film,frame and/or adhesives areas to directly reduce the thermal build up inthese materials, shown in FIG. 8. A top flow 20, side flow 21 or abottom flow 22 of coolant can be utilized to control temperature. Thistypically does not only reduce the risk of pellicle film damage but alsotypically reduces the risk of creating contaminating out-gassing fromthe pellicle frame and pellicle film adhesives. In addition to hardwarecontrol of the system thermal buildup, it is possible to reduce thermalbuild up by allowing for an increased process time. Applying a slowerrate of pulses to the system or allowing a delay between a series ofpulse application can allow the injected heat to be removed without thetotal system temperature rising above a critical level.

Pulse to pulse thermal build up may also advantageously be controlledand may depend on the thermal characteristics of the contamination,substrate and/or adjacent materials. In general, pulse to pulse thermalbuild up can be controlled by reducing the number of laser pulseshitting the surface per unit time. This temperature build up can also becontrolled by increasing the distance between adjacent laser pulses. Itmay be particularly desirable to have a large lateral displacementbetween adjacent pulses, where the material is particularly sensitive topulse-to-pulse thermal build (e.g., pellicle film materials). In thiscase, the process typically involves positioning the laser beam atnearly the same locations multiple times to obtain full cleaning of thetarget surface. For example, a first series of laser pulses 13 areexposed to the surface 4 with a relatively large lateral separation asshown in FIG. 9A. A second pass over the same area places an additionalseries of laser pulses 13 that are slightly shifted relative to thefirst set of spots as shown in FIG. 9B. This process continues until theentire area has been exposed to the laser pulses 13 as shown in FIG. 9B.Overlap in a second direction can be used, according to certainembodiments of the present invention, to completely expose a substratesurface 4 is illustrated in FIG. 9D. According to certain embodiments ofthe present invention, this overall process is repeated an/or theoverlap between passes is increased, particularly if it is desirable forthe cleaning process to include multiple pulses for complete removal.Changing the position of the beam relative to the surface as illustratedcan be accomplished by moving the beam and/or moving the substrate. Inaddition, applying pulses in a more systematically distributed manneracross the mask may reduce further the likelihood of heat buildup on themask as illustrated in FIG. 9E.

Residue Control

According to certain embodiments of the present invention, the lasercleaning method may produce residual materials on the photomask surfacedepending on the decomposition products of the contamination. Even ifthe residues no longer affect the use of the substrate material (i.e.,even if the substrate is effectively cleaned), there may still be areason to control their location or concentrations. Traditional methodsfor controlling residue formation such as, for example, applying adirected airflow, water flow or creating a reduced pressure over thesubstrate to be cleaned may be used according to certain embodiments ofthe present invention. However, for the case of an enclosed system, suchas for example a pellicalized photomask, it is typically not desirableto use these environmental controls. As such, alternative methods forcontrolling the location of residual materials are used for a closedsystem according to certain embodiments of the present invention. Forexample, according to certain embodiments of the present invention, thepattern of laser pulses is controlled. For example, FIG. 10 shows anembodiments where the pattern of laser pulses 13 starts in the center ofthe substrate's 4 surface and is directed into an increasing diametercircular or increasing dimension square pattern 23, residual materialwill be preferentially moved toward the edges of the substrate as shownin FIG. 10. Another method according to certain embodiments of thepresent invention to control residue is to utilize gravity. Placing thephotomask with the surface facing down is shown in FIG. 11A or tiltedposition 24 as illustrated in FIG. 11B, allowing for preferentialdeposit of residue materials on the pellicle film, or side of thephotomask, respectively. In another method the reticle could be rotated(i.e. spun) in conjunction with certain embodiments of the presentinvention to cause residual materials to move away from the mask centerand/or to non-active areas on the reticle. In addition, reducing thetemperature of an area of the photomask, pellicle, pellicle frameaccording to certain embodiments of the present invention, createspreferential depositing of residue material to these surfaces, sincethis material is likely to be generated from a vapor phase transition toa liquid or solid as shown in FIG. 8. For example, these cooling methodscould include but are not limited to flowing of water, other fluids orgases, thermal-electric cooling, or laser induced cooling in and/oraround the preferred deposition areas.

Mitigation of Haze Growth and Reformation

The current invention could be used in conjunction with surfacepreparation or environmental control techniques to extend reticlelifetime. Some of these techniques will require processing beforepellicle mounting while others can be performed post-pellicalization.For example, a surface preparation method in conjunction with thepresent invention prior to pellicilization could increase the timebetween cleanings. This could be important if there are a limited numberof the inventive method cleans possible before additional cleaning (egg.Wet clean) is required. One embodiment of this inventive method is toplace seed crystals or other nucleating materials beneath the pelliclein non-active areas of the reticle. These seed crystal may act aspreferential growth sites for haze. This may effectively reduce theconcentration of residues and precursor materials available to theactive areas of the photomask and reduce growth rates in these areas.Another embodiment of this method is to coat the surface of the maskwith a material that reacts with and/or neutralizes the residues andprecursor materials liberated by the inventive cleaning process. Thismay also reduce haze growth rates in the active areas on the mask bylimiting the available reactive species.

Post pellicle techniques could also be used in combination with thepresent invention. For example, environmental control or manipulationboth inside and outside the pellicle could be used in combination withthe present cleaning process invention. One embodiment would includeexchanging the environment under the pellicle with a non-reactive gasafter clean processing. This could be performed without pellicle removalby gas exchange through a filtered vent on the pellicle frame. It may beadditionally advantageous to maintain an inert environment outside ofthe pellicle in conjunction with the present invention to mitigate hazere-growth or reformation. These combination processes could extend thetime between clean processing with the inventive method and may beimportant if a limited number of clean processes can be used.

An additional post-pellicle, environmental control embodiment of thecurrent invention would evacuate the environment under the pellicle andintroduce or exchange the environment with a material that reacts withor neutralizes haze residues and/or precursors. This process could beperformed before, during or after clean processing. In all cases, thehaze residues and/or precursor species liberated during the cleanprocess would react with the introduced/exchanged material to create anon-haze forming species.

Additional post pellicalization techniques could be used in conjunctionwith the present invention to mitigate haze re-growth or reformation.These techniques would utilize the thermal effects of the presentinvention to alter surface morphology and/or substrate composition toinhibit haze growth and reformation. For example, operating at or nearthe quartz reflow temperature may produce a change in the material stateor morphology of the quartz substrate. This could reduce or eliminatethe activation sites believed to cause nucleation of crystalline hazegrowth and thereby reduce the rate of haze growth or reformation. Analternative embodiment would combine surface preparation orenvironmental control method in combination with the thermal affect ofthe inventive method to modify or eliminate activation/nucleation sites.The precursor materials could be activated by thermal processing orcould react with the surface under thermal excitation to reduce hazegrowth and reformation.

Metrology

Methods according to certain embodiments of the present invention mayalso be used in combination with metrology to monitor the criticalprocess parameters and/or to evaluate the progression or completion ofthe cleaning process. Measurement of the locally generated temperatureof the substrate materials can, for example, be used in combination withthe cleaning process. Temperature measurement can be evaluated prior toapplication of the cleaning process in order to verify risk oftemperature related damage. In addition, these temperatures may bemonitored during the cleaning process to verify process control and/orreduce the risk of material damage. For example, according to certainembodiments of the present invention, the temperature of the substrateand/or absorber film is monitored during the process and has the abilityto feed back control of the energy applied to maintain the desiredprocess or turn off the cleaning process if too large a temperaturebuild up is detected. Multiple methods of temperature monitoring existare shown in FIG. 12 and include contact, for example, thermal-couple 26and non-contact, for example, infrared camera 25 techniques.

Metrology is also used, according to certain embodiments of the presentinvention, to analyze the contamination for material properties priorto, during and/or after the removal process, shown in FIG. 13.Identification of the contaminant prior to running the cleaning processmay be used to set the ideal processing parameters. This allows use ofthe minimum process temperature, thereby reducing the risk of substratedamage. Monitoring the contamination during the process may also be usedto assess the completion of the cleaning process based on the strengthof the measurement signal as the cleaning process progresses. Inaddition, monitoring for alternative materials during the process may beused to signal when the process is creating a different contaminationand/or causing an undesired change in the substrate material. Thisinformation may be used to control the process and/or to reduce the riskof substrate damage and/or a poor cleaning result.

Metrology is also used, according to certain embodiments of the presentinvention, to analyze or monitor the material properties of thesubstrate 4 and/or materials on or adjacent to the substrate prior to,during and/or after the removal process as shown in FIG. 13. Forexample, measurement of the material properties of a partial absorberfilm on the substrate can be used to calculate the phase delay of thematerial before processing. This could be used to determine the processtemperature for cleaning in order to induce an appropriate phase delayin absorber film. This metrology could also be used to monitor the phaseduring processing and feedback information to the process or stop theprocesses if it is outside a process limit. Material property analysisof the substrate could be used to determine the correct energy to inducea desired surface material or morphology change. In addition, thematerial properties of the pellicle film could be monitored to determineif an adverse affect is occurring to the pellicle material. Thisinformation could be used before processing to limit processtemperature, or during processing to stop the process if damage isobserved. For example, one or more ellipsometers or cameras 31 could beused to measure the material response of the pellicle film, absorberfilm and substrate surface. This data can then be used to calculate thedesired material properties including film thickness, transmission andphase.

Alternative metrologies to monitor the presence and amount of surfacecontamination can be used prior to, during and/or after the cleaningprocess according to certain embodiments of the present invention. Forexample, metrology used to detect the presence of contamination may beused according to certain embodiments of the present invention todetermine whether or not to apply laser pulses to the region of thesubstrate that was measured. This information may then be used tominimize the number of pulses applied to the overall substrate whichreduces the total thermal energy applied to the system as well as theoverall cleaning process time.

Metrology to measure the lateral size/dimensions, location, number,density and/or height (thickness) of the contamination or contaminatingparticles can also be used, according to certain embodiments of thepresent invention, in combination with the cleaning process. Thesemeasurements can, for example, be used to qualify the efficiency andcompletion of the process by measurement before and/or after thecleaning process. During the process, these measurements can be used toevaluate the in-situ efficiency of the processes. For example, ifmultiple laser pulses are used for complete removal, detection ofremaining contamination can be used to evaluate the number of pulsesrequired for removal and if additional pulses are necessary. In thiscase, the metrology, according to certain embodiments of the presentinvention, is configured to view the area being cleaned while thecleaning process is occurring. This is typically done by imaging thearea being exposed by the laser and can include the use of the sameoptics used for laser delivery as shown in FIG. 14. An imaging lens 32allows detailed surveillance of the contaminating particulate 3 througha partially reflective mirror 29, permitting simultaneous monitoring andcleaning.

Multiple methods exist according to embodiments of the present inventionfor detection of particles and evaluation of particle dimensions. Thesemethods include, for example, reflected and transmitted light intensitymeasurement, imaging, low angle scattered light detection,interferometry, scanning electron beam, scanning tunneling microscopy,near field microscopy, atomic force microscopy, etc. Multiple methodsmay be combined according to certain embodiments of the presentinvention to provide additional information.

In the case of a photomask, for example, multiple metrologies may beincorporated into the laser cleaning process according to certainembodiments of the present invention. Identifying the presence of aspecific contamination (e.g., ammonium sulfate) on a photomask, forexample, defines the decomposition temperature requirement and sometimesallows selection of laser energy just high enough to perform thecleaning process.

According to certain embodiments of the present invention, transmittedlight intensity is measured and the result is compared with theprogrammed structure for the absorbing film on the photomask surface.Discrepancies between programmed features and detected features are thenused to identify contamination. In addition, Aerial Imaging Measurementis used according to certain embodiments of the present invention toevaluate the print characteristics of the photomask. This method istypically used to evaluate the effect of contamination on theperformance of the photomask. This measurement can also be used in-situto detect damage to the absorber layer resulting from the clean process.This is particularly relevant for partially absorbing films in which thethickness of the film has a direct relationship to the photomaskperformance. According to certain embodiments of the present invention,combining scattered light detection with transmitted light detectionimproves identification of contamination by detecting irregular surfacetopography which would differ from the typically smooth surface of thephotomask and photomask film.

Metrology is also used according to certain embodiments of the presentinvention to monitor the characteristics of materials adjacent to thesurface being cleaned. For example, the temperature of a pellicle filmabove a photomask may be monitored to reduce the risk of pellicle filmdamage. The transmission characteristics of the pellicle film can alsobe used to qualify the affects of the cleaning process during or afterthe clean process. In addition, detection of particulates on the insideof the pellicle film may be made prior to performing the clean processand/or may be used to detect loss of these particles during the processand/or whether or not there should preferably be a limit of the energyused on the process to prevent the risk of pellicle and/or substratematerial damage.

As will be appreciated by one of skill in the art upon practicing one ormore embodiments of the present invention, the metrology examplesdiscussed above are not intended to be all inclusive of the presentinvention. Rather, these examples merely illustrate the use of metrologywithin some methods according to the present invention.

Apparatus

Certain methods according to embodiments of the present invention areincorporated into apparatuses used to perform the laser surface cleaningprocess. An example of such an apparatus is shown in FIG. 15,additionally include a robot 35 for handling of the substrate materialwith a robot end effector to precisely position the substrate materialand a platform 34, for one or more axes of motion to position thesubstrate sample relative to the laser beam. The apparatus may, forexample, contain one or more of the metrologies as described aboveand/or may include ways of controlling the temperature of the substrateand/or adjacent materials during the cleaning process. In addition, theapparatus may include metrology used to register the substrate to thestaging system and therefore to the laser beam. This metrology may alsoinclude computer controlled vision recognition systems. Further, theapparatus may also utilize computer control of the laser, motion and/ormetrology and may provide for software based recipe control of thecleaning process. Laser control may, for example, include controllingwhen laser pulses are applied as well as the amount of energy appliedduring the cleaning process.

Wafer Fabrication Process

A method and/or apparatus according to certain embodiments of thepresent invention can be used as part of a novel wafer fabricationprocess that includes the removal of haze formation from a pellicalizedphotomask surface. Typically, photomasks are taken out of the waferprint process when the level of haze has become enough to adverselyaffect the wafer print process. The time before photomasks are taken outis typically determined either by direct detection of a high level ofhaze contamination or is based on a pre-determined duration and/or levelof use in the wafer process. Typically, the photomask is sent to adifferent facility to have the pellicle removed, photomask cleaned andanother pellicle attached to the photomask. These other facilities(e.g., mask shops) maintain the equipment required to accomplish thesetasks as well as to perform photomask repair and additional inspectionsnot required at a wafer fabrication facility. Duplicate sets ofphotomasks are typically used during the time required to have thephotomasks cleaned and a new pellicle attached. These additionalphotomasks add a significant cost to the overall wafer print processbecause of the high material and setup and evaluation costs required.

A novel wafer fabrication method according to certain embodiments of thepresent invention incorporates an apparatus utilizing one or more of themethods discussed above to clean a photomask surface of haze. A typicalwafer fabrication process according to an embodiment of the presentinvention illustrates the use of wet clean processing to removephotomask contamination is shown in FIG. 16A. An alternative method alsowithin the scope of certain embodiments of the present inventionutilizes one or more of the laser cleaning methods described above toperform the cleaning operation at the wafer fabrication facility andwithout pellicle removal is shown in the flowchart FIG. 16B This canminimize or eliminate the additional pellicle costs and/or deteriorationof the photomask film produced by the current wet clean processing.

According to certain embodiments of the present invention, a novel waferfabrication process eliminates the use of additional masks or mask setsfor product manufacture while the original set is being cleaned. In thismanufacturing process, the original photomask(s) are placed immediatelyback into production following the cleaning process is shown in theflowchart FIG. 16C. This has the potential of eliminating duplicate masksets as well as decreasing the required setup times for using duplicatemask sets. The use of inspection metrology to verify the cleaningprocess may be advantageously used prior to returning the photomask backinto production. This measurement may, for example, be incorporated intothe apparatus or provided by an additional apparatus at the waferfabrication or other facility. Regardless, of the metrology, the overallprocess time for the photomask haze removal will be reduced.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

1. A method for laser surface cleaning, the method comprising: directinga laser towards a substrate with a contaminant, the substrate includinga surface upon which a patterned, thin film layer is disposed such thatportions of the surface have no thin film coating; producing a firstlocal thermal increase in said substrate surface with said laser suchthat a temperature of the substrate surface and a temperature of thethin film layer are similar at the locality; inducing a second thermalincrease in said contaminant at the locality due to said first thermalincrease in said substrate surface; and producing a thermaldecomposition of said contaminant.
 2. The method in claim 1 in whichsaid substrate's temperature remains below a temperature in which damageor detrimental effects will occur to said substrate.
 3. The method inclaim 1 in which said substrate's temperature remains below atemperature in which damage or detrimental effect will occur tomaterials disposed relative to the substrate.
 4. The method of claim 1in which said substrate's temperature remains below a temperature inwhich damage or detrimental effect will occur to a device or a productthat incorporates said substrate.
 5. The method of claim 1 wherein themethod is a dry laser surface cleaning method.
 6. The method of claim 1wherein the substrate is a photomask.
 7. The method in claim 1 in whichthe laser's output is pulsed.
 8. The method in claim 1 in which thelaser's output is pulse width varied.
 9. The method in claim 1 in whichthe substrate is partially or completely enclosed or protected by apellicle.
 10. The method in claim 1 in which the laser is directedthrough a material disposed relative to the substrate.
 11. The method inclaim 1 in which the laser's wavelength is selected to permit absorptionof the laser's energy by the substrate.
 12. The method of claim 1 inwhich one or more lasers of different wavelengths or a tunable laser isutilized thereby permitting heating of the substrate when the substrateis composed of at least two materials.
 13. The method in claim 1 inwhich a heat sink is positioned adjacent to the substrate to permitcooling.
 14. The method in claim 1 in which the substrate is physicallymanipulated or oriented to mitigate the effects of residual or resultantmaterials.
 15. The method of claim 1 in which the substrate is cooledvia convection.
 16. The method of claim 1 in which one or moremetrologies are used in conjunction with the cleaning process.
 17. Themethod in claim 1 in which the laser contributes directly to the thermalincrease in the contaminant.
 18. A method for mitigating the effects ofcontamination on a substrate including a surface upon which a patterned,thin film layer is disposed such that portions of the surface have nothin film coating, the method comprising: employing an energy source toproduce a first local thermal increase in said substrate surface, suchthat a temperature of the substrate surface and a temperature of thethin film layer are similar at the locality, which induces a secondthermal increase in said contaminant at the locality resulting inthermal decomposition of said contaminant.
 19. The method in claim 18,wherein the energy source is external to the substrate.
 20. The methodin claim 18, wherein the energy source is an electromagnetic energysource.
 21. The method in claim 18 wherein the energy source is a laser.22. The method in claim 18 in which the substrate's temperature remainsbelow a temperature in which damage or detrimental effect will occur tothe substrate.
 23. The method in claim 18 in which the substrate'stemperature remains below a temperature in which damage or detrimentaleffect will occur to materials disposed relative to the substrate. 24.The method of claim 18 in which the substrate's temperature remainsbelow a temperature in which damage or detrimental effect will occur toa device or product that utilizes the substrate.
 25. The method of claim18 wherein the substrate surface is dry.
 26. The method of claim 18wherein the substrate is a photomask.
 27. The method in claim 18 inwhich a heat sink is positioned adjacent to the substrate to permitcooling.
 28. The method in claim 18 in which the external energy sourcecontributes directly to the thermal increase in the contaminant.
 29. Themethod of claim 18 in which one or more metrologies are used.
 30. Themethod in claim 18 in which the substrate is physically manipulated ororiented to mitigate the effects of residual or resultant materials. 31.A method for mitigating the effects of contamination on a substrateincluding a surface upon which a patterned, thin film layer is disposedsuch that portions of the surface have no thin film coating, the methodcomprising: directing an energy source through a material disposedrelative to the contaminant to produce a first local thermal increase insaid substrate surface, such that a temperature of the substrate surfaceand a temperature of the thin film layer are similar at the locality,which induces a second thermal increase in said contaminant at thelocality resulting in thermal decomposition of said contaminant.
 32. Themethod in claim 31 wherein the energy source is focused toward thesubstrate surface.
 33. The method in claim 31, wherein the energy isprovided by an electromagnetic energy source.
 34. The method in claim 31wherein the energy source is a laser.
 35. The method of claim 34 inwhich the laser's output is pulsed.
 36. The method of claim 34 in whichthe laser's pulsed output is width varied.
 37. The method of claim 34 inwhich the laser's wavelength is selected to permit absorption of thelaser's energy by the substrate's surface.
 38. The method of claim 34wherein the substrate is a photomask.
 39. The method of claim 31 whereinthe material disposed relative to the contaminated surface is a pellicleframe and film.
 40. The method of claim 31 wherein the material disposedrelative to the contaminated surface absorbs energy from the externalenergy source.
 41. The method of claim 31 wherein a means for reducingthermal increase in the material disposed relative to the contaminatedsurface is provided.
 42. The method of claim 41 wherein the means is aform of forced convection.
 43. The method in claim 31 in which thesubstrate is physically manipulated or oriented to mitigate the effectsof residual or resultant materials.